Inherited renal cystic diseases, including the various forms of polycystic kidney disease (PKD) are prevalent conditions that usually affects multiple organs. There are numerous human genes, which when mutated, lead to a variety of cystic phenotypes with variable extrarenal manifestations. There are several rodent models, some with mutations in known human PKD genes. Others models represent rodent PKD genes, but could also function as modifier genes for other rodent models and human PKD. However, all of these models have made important contributions to our knowledge of PKD. The present proposal will isolate the rat wpk gene which causes renal changes similar to human autosomal recessive PKD. Additionally, affected rats have a cerebral defect (hydrocephalus with agenesis or hypoplasia of the corpus callosum) similar to that seen in human oro-facial-digital, genitopatellar and cerebro-renal-digital syndromes. Currently we localized the wpk gene to a 2Mb region of rat Chromosme 5, a location known to harbour a rodent PKD modifier locus and about 20 genes. The long term goal of our research is to identify genes and pathways involved in renal cystogenesis in order to develop therapeutic interventions. We hypothesize that the Wpk gene represents a human PKD gene and/or a modifier locus. Our Specific Aim is to: 1) Identify, clone and characterize the Wpk gene by crossing the Wistar-wpk rat with inbred Brown Norway rats and using chromosomal markers to localize the gene. Aside from the positional approach, we will identify candidate genes from with the 2Mb regions to test using RT-PCR as well as by screening rat ESTs from that region. Once identified, 9organ expression and immunohistochemistry will be used to identify the tissues and cells that express this gene product. The identification of the Wpk gene and its protein product will allow insight into cystogenesis as well as important information on shared pathways in kidney and brain development. This model and the Wpk gene are important for 2 major reasons, a) they have cystic disease and unique cerebral pathology similar to a few human conditions and b) the Wpk lies in a chromosomal region known to modify other rodent forms of PKD and may be an important modifier locus for PKD (rodent and human).